polι-dependent lesion bypass in vitro

Abstract Based upon phylogenetic relationships, the broad Y-family of DNA polymerases can be divided into various subfamilies consisting of UmuC (polV)-like; DinB (polIV/polκ)-like; Rev1-like, Rad30A (polη)-like and Rad30B (polι)-like polymerases. The polIV/polκ-like polymerases are most ubiquitous, having been identified in bacteria, archaea and eukaryotes. In contrast, the polV-like polymerases appear restricted to bacteria (both Gram positive and Gram negative). Rev1 and polη-like polymerases are found exclusively in eukaryotes, and to date, polι-like polymerases have only been identified in higher eukaryotes. In general, the in vitro properties of polymerases characterized within each sub-family are quite similar. An exception to this rule occurs with the polι-like polymerases, where the enzymatic properties of Drosophila melanogaster polι are more similar to that of Saccharomyces cerevisiae and human polη than to the related human polι. For example, like polη, Drosophila polι can bypass a cis - syn thymine–thymine dimer both accurately and efficiently, while human polι bypasses the same lesion inefficiently and with low-fidelity. Even in cases where human polι can efficiently insert a base opposite a lesion (such as a synthetic abasic site, the 3′T of a 6-4-thymine–thymine pyrimidine–pyrimidone photoproduct or opposite benzo[ a ]pyrene diol epoxide deoxyadenosine adducts), further extension is often limited. Thus, although polι most likely arose from a genetic duplication of polη millions of years ago as eukaryotes evolved, it would appear that polι from humans (and possibly all mammals) has been further subjected to evolutionary pressures that have “tailored” its enzymatic properties away from lesion bypass and towards other function(s) specific for higher eukaryotes. The identification of such functions and the role that mammalian polι plays in lesion bypass in vivo, should hopefully be forthcoming with the construction of human cell lines deleted for polι and the identification of mice deficient in polι.